Aerobic Exercise-induced Anabolic Responses After Inhibition/stimulation Of Hpa Axis In Healthy Adults

Abstract

Exercise is a stress stimulus leading to endocrine changes in the human body. There are interactions between the Hypothalamo-Pituitary-Adrenal (HPA) axis components in response to exercise, depending on the characteristics of exercise (type, duration, intensity, and frequency). Anabolic responses after aerobic exercise are less predictable yet important to explore. PURPOSE: This study examined the anabolic factor insulin-like growth factor-1 (IGF-1) responses to a selected aerobic exercise protocol performed under inhibition or stimulation of the HPA axis in healthy volunteers. METHODS: Twelve healthy volunteers (8 males and 4 females, age: 30.6 ± 4.4 yrs, body mass: 77.3 ± 12.3 kg, height: 1.77 ± 0.07 m) performed a single bout of 30 min aerobic exercise at 70%VO2 max on a treadmill, on three different conditions [control (C), HPA axis inhibition (HPA-I, induced by glucocorticoid administration), HPA axis stimulation (HPA-S, induced by ACTH administration)], following standard diet. Blood samples were collected before (PRE) and at the end of the exercise bout (POST) and serum IGF-1 was measured with ELISA. Two-way ANOVA was used for statistics and data is presented as mean ± SE. RESULTS: In C condition, IGF-1 did not change post-exercise (189.4 ± 24.3; 191.6 ± 17,9 ng/mL; at PRE and POST, respectively). Under HPA-I condition, decreased levels of IGF-1 were observed at the end of exercise (212.6 ± 18.7; 155.2 ± 20.5; ng/mL; at PRE and POST, respectively), however this decrease failed to reach statistical significance (p > 0.05). Inversely, under HPA-S condition IGF-1 exhibited a trend to increase 30 min after exercise (p > 0.05) (141.8 ± 13.9; 156.1 ± 18.1 ng/mL; at PRE, and POST, respectively). Under HPA-S condition, IGF-1 levels were significantly lower compared to HPA-I condition at PRE (141.8 ± 13.9 vs 212.6 ± 18.7; p < 0.05). However, there were no significant differences in serum IGF-1 concentrations between the three conditions as a result of exercise, or between males and females. CONCLUSION: IGF-1 did not seem to change immediately after moderate aerobic exercise regardless of the inhibition or stimulation of the HPA axis. However, the modification of HPA axis found to affect IGF-1 levels at rest. Further studies are needed to characterize the IGF-1 responses during the recovery period after aerobic exercise.